In the marketplace of sensors generally, there is a growing demand for smart sensors, such as in the consumer electronics industry, automotive industry, healthcare industry, and in some industrial sectors such as textile, material manufacturing, and Food and beverage (F&B) among others. Generally speaking, sensors are preferred to be small in size, light in weight, non-intrusive, and to have low power consumption.
Wireless sensors operating with a sensor network are often desirable to monitor various parameters. Eliminating cable requirements makes such sensors easy for installation and deployment. For example, temperature and humidity sensors are widely used to monitor and optimize the operation of heating, ventilation and air conditioning (HVAC) in the building automation industry. Accelerometers are commonly utilized for health monitoring in consumer electronics industry. While commercially available wireless sensors exist today, the costs of current platforms are still high (for example, possibly about $25-$250/node), and the service lifetimes of required batteries are still relatively short. A main cost contributor to such sensor nodes are their on-board battery components. In addition to time consumption, maintenance such as battery replacement involves much labor cost. Thus, better wireless sensors with relatively lower costs (for example, under $10/node), providing multi-functions, and requiring less maintenance, are highly desired.
Sensors operable in relatively harsh environments are important in certain circumstances, such as in aerospace and downhole applications, where for example high temperature and high pressure environments may degenerate operations or even disable such sensors. For example, temperatures outside satellites or space vehicles can go below 3 degrees Kelvin, in which case conventional electrical devices can't survive.
Typically, a transducer can work under hard conditions, while a signal conditioner and processor works at normal conditions. Therefore, an unconditioned signal is too weak to be transmitted out of a harsh zone and still achieve less distortion and loss. Improved sensor technology is desired for better addressing such technical problems.
For harsh environment sensors, transducers may be typically be provided in the sensing environment, while the ADCs (analog to digital converters) and digital processors may be isolated from the sensing environment, as referenced herein. As such, the analog signal path from the transducer to the ADC could be affected by noise in the harsh operating environment, leading to an undesirably low signal to noise ratio (SNR).
Generally speaking, chipless radio-frequency identification (RFID) tags are RED tags that do not require a microchip in a transponder. Such tags contain electronically stored information, which is detected by being read through the use of electromagnetic fields. For example, such a device backscatters the signal from the reader without a protocol control system. One benefit is that a powerless feature is achieved, which can be utilized to fabricate relatively low-cost passive sensors. One example of a chipless RFID tag and method for communicating with the RFID tag is represented by U.S. Pat. No. 8,068,010. Another example of a chipless passive RFID tag is represented by U.S. Pat. No. 8,556,184. The complete disclosures of such patent documents are incorporated by reference herewith, and for all purposes.
Chipless RIM may be generally classified into time-domain reflectometry and frequency signature techniques. In time domain reflectometry, the interrogator or reader sends a pulse and listens for echoes. The timing of arrival pulses encodes the binary data. Among the time domain reflectometry, surface acoustic wave based RFID tag is sometimes of interest for some applications because it has relatively low loss. In frequency signature RFIDs, the interrogator sends waves with several frequencies, a broadband pulse or a chirp, and detects the echoes' frequency content. The presence or absence of certain frequency components in the received waves encodes the data. With the same method, it is possible to inscribe the transducer signal on a time or frequency domain.
In other circumstances, the need for relatively high sensor sensitivity can require a signal detection instrument associated with the sensor (e.g. vector network analyzer) to have a large dynamic range (DR). For instance, a network analyzer may need to operate at a DR better than 120 dB. Such a relatively large dynamic range can cause environmental interference, such as mechanical vibrations and/or scattered RF radiations, which can destabilize, for example, interferometer operations. Therefore, in such example, a need exists for a simple, robust RF sensor that can simultaneously provide both increased sensitivity and lower system DR requirements.